When a truck is provided with air-suspension, it is necessary that the compressed-air supply system of the vehicle has sufficient capacity to allow quick and efficient loading and unloading cycles. Large amounts of compressed air are consumed, particularly when connecting and disconnecting swap bodies and so called trailers, or semi-trailers. However, at the same time the compressed-air system must primarily have sufficient capacity to meet the demand of compressed air for the vehicle's brake system.
Trucks having air-suspension are usually provided with special high pressure compressors and with high pressure tanks for the air-suspension system containing up to 110 liters of air. The air-suspension system is supplied with compressed air at an air pressure of between 7 bar up to 12 bar. The brake system operates at a considerably lower air pressure, between 5 bar and 7.5 bar. For this reason, the vehicle must be provided with separate air supply systems and separate compressed-air tanks for the brakes and the air-suspension. Furthermore, the vehicle's brake system comprises special compressed-air tanks for the front and the rear brake circuit, respectively. Taken together, this implies that conventional trucks with air-suspension usually have about eight air tanks which must be built into the chassis of the vehicle. In order to achieve this, a very complicated and expensive design of the chassis is required, since, of course, the available space is limited.
Moreover, the many air tanks require that space, which otherwise could be used for transporting goods, must be reserved for storage of compressed air. In addition, the weight of the air tanks detracts from the weight of the goods which may be transported by the vehicle.
However, with the present invention a compressed-air system of the type mentioned in the introduction has been achieved, offering the possibility of reducing the number of compressed-air tanks.
The compressed-air system in accordance with the invention is primarily distinguished by the compressed-air tank being dimensioned for an air pressure which is greater than or equal to the air pressure which is demanded in the air-suspension system and further by the compressed-air tank being connected to both the air-suspension system and the brake system and comprising compressed-air conduits through which compressed air can pass by way of one or more outlets in the compressed-air tank to the brake system and the air-suspension system, respectively, wherein a pressure-limiting valve is arranged downstream of the outlet to the compressed-air conduit(s) connecting the compressed-air tank with the brake system.
By using a compressed-air system in accordance with the invention, it is possible to largely utilize the same air tanks for the air supply to the brake system as for the air-suspension. Hereby, the number of compressed-air tanks which is required to supply a vehicle with compressed air may be reduced by one or several tanks. By storing compressed air at a pressure of 12 bar in the brake air tanks, the air can be used in the upper pressure region for the air-suspension and in the lower pressure region for the brake system.
This is preferably achieved by the use of a seven-port protection valve having four compressed-air circuits. Further, pressure limiting valves are employed in order to obtain a lower pressure in the respective front and rear brake circuits of the vehicle.
For certain types of goods vehicles having a rear overhang, it is possible to omit the compressed-air tank which, when using a conventional compressed-air supply system, is placed in the overhang. Hereby, it is also possible to omit the cross-bar on which the compressed-air tank is mounted, whereby the overhang can be shortened. This results in a saving of both weight and space.